1. Field of the Invention
The present invention relates to a printed circuit board unit with a cooling device in general incorporated within an electronic apparatus such as a portable digital assistant (PDA), a notebook personal computer, and the like. In particular, the invention relates to a printed circuit board unit comprising a printed circuit board, a ventilation fan rotatable around the rotation axis intersecting the printed circuit board, and a fan housing accommodating the ventilation fan.
2. Description of the Prior Art
As disclosed in Japanese Patent Application Publication P2000-77877A, a so-called fan unit includes a fan housing accommodating a ventilation fan rotating around the rotation axis. When the ventilation fan rotates, air is allowed to flow in the centrifugal direction of the rotation axis. The fan housing serves to guide the air toward the outlet. The air is discharged out of the outlet. At the same time, air surrounding the fan housing is introduced into the fan housing through the inlet. The inlet is defined to face the surface of the printed circuit board. When the air is sucked into the fan housing, air is allowed to flow along the surface of the printed circuit board.
In general, a number of electronic components are mounted on the surface of the printed circuit board. The respective electronic components protrude from the surface of the printed circuit board, so that the electronic components hinder a smooth flow of the air. The turbulence in the air is supposed to constrain the ventilation fan from sucking the air into the fan housing. The suction quantity of the air may be reduced. The ventilation fan suffers from reduction in the cooling efficiency. As the printed circuit board gets thinner, the space is reduced between the fan housing and the surface of the printed circuit board. The cooling efficiency of the ventilation fan may still get deteriorated.
It is accordingly an object of the present invention to provide a printed circuit board unit with a cooling device contributing to reduction in the thickness of an electronic apparatus.
According to the present invention, there is provided a printed circuit board unit with a cooling device, comprising: a printed circuit board; a ventilation fan rotating around a rotation axis intersecting the printed circuit board; a housing wall standing from a surface of the printed circuit board at a periphery of the ventilation fan; and an outlet defined in the housing wall.
The printed circuit board and the housing wall cooperate to define a space for accommodating the ventilation fan. When the ventilation fan rotates, the movement of air, namely, airflow can be generated within the space. The printed circuit board and the housing wall lead the air toward the outlet. In this manner, the printed circuit board can be utilized to form the cooling device.
In particular, a high speed airflow can be generated within the space in the printed circuit board unit and the housing wall. The airflow efficiently absorbs the heat from the surface of the printed circuit board. The heat radiation from the printed circuit board can be promoted. In general, an electrically conductive metallic wiring pattern extends over the surface of the printed circuit board. The metallic wiring pattern usually has a superior heat conductivity as compared with the material of the printed circuit board. The metallic wiring pattern thus contributes to promotion of the heat radiation from the printed circuit board. In particular, the metallic wiring pattern inside the housing wall leads to an improved promotion of the heat radiation from the printed circuit board.
The printed circuit board unit of the aforementioned type may further comprise: a ceiling wall connected to an upper end of the housing wall and extending along a datum plane parallel to the surface of the printed circuit board; and an inlet defined in the ceiling wall.
In general, a number of electronic components are mounted on the surface of the printed circuit board. The electronic components protrude from the surface of the printed circuit board. The electronic components is supposed to hinder a smooth flow of the air along the surface of the printed circuit board. If the inlet is defined at a position spaced from the surface of the printed circuit board in the aforementioned manner, a smooth flow of the air can be established irrespective of the existence of the electronic components. The air can smoothly be sucked into the inlet. A large quantity of the air can be sucked, so that the cooling efficiency of the cooling device can be improved.
For example, if the printed circuit board of the aforementioned type is incorporated within an electronic apparatus, the inlet can be opposed to the inner surface of the enclosure of the electronic apparatus. Airflow can be generated along the inner surface of the enclosure in response to the suction of the air into the inlet. In general, a generally flat surface is defined on the inner surface of the enclosure. Less obstacles can be found on the inner surface of the enclosure as compared with the surface of the printed circuit board. A smooth airflow can thus be generated along the inner surface of the enclosure. The air is smoothly sucked into the inlet. Since the air is smoothly introduced into the inlet in this manner, a higher cooling efficiency can be kept even when the space is reduced between the inlet and the inner surface of the enclosure in the electronic apparatus. The thickness of the electronic apparatus can reliably be reduced.
The printed circuit board unit of the aforementioned type may further comprise an inlet defined in the printed circuit board inside the housing wall. Air can be introduced not only from the space adjacent the front side of the printed circuit board but also from the space adjacent the back side of the printed circuit board. A larger quantity of air can be sucked into the space defined by the printed circuit board and the housing wall, so that the cooling efficiency of the cooling device can further be improved. Moreover, the front and back sides of the printed circuit board can simultaneously be cooled down enough. It should be noted that the inlet in the printed circuit board may be established in place of the inlet in the ceiling wall. This structure contributes to a further reduction in the thickness of the electronic apparatus.
In addition, the printed circuit board unit of the aforementioned type may further comprise: an electronic component mounted on the printed circuit board; and an electrically conductive wiring pattern extending over the surface of the printed circuit board inside the housing wall and connected to the electronic component. The ventilation fan serves to promote the heat radiation from the electrically conductive wiring pattern. The heat radiation from the printed circuit board can still be improved. Moreover, since the electrically conductive wiring pattern is allowed to receive the heat from the electronic component, the electronic component can efficiently be cooled down.
A heat radiation fin may be attached to the printed circuit board and connected to the electronic component. The heat radiation fin promotes the heat radiation from the electrically conductive wiring pattern. The heat radiation fin may be located within the outlet. Alternatively, the heat radiation fin may be located to face the outlet.
An electronic component may be mounted on the printed circuit board inside the housing wall. A high speed airflow can be generated inside the housing wall based on the rotation of the ventilation fan in the aforementioned manner. Accordingly, the electronic component can efficiently be cooled down. The electronic component may be located within the outlet, for example.